1. Field of Invention
This invention pertains to a device used, in conjunction with a rope, to stop a falling object and/or to lower an object in a controlled manner. In particular it pertains to a belay device and, more specifically, to an auto-locking belay device. The subject invention has application in the sport of rock climbing and in certain industrial applications for fall protection.
2. Prior Art
In the sport of rock climbing, a belay device is used to protect a climber from injury in the case of a fall. Generally the climber wears a harness to which one end of a rope is attached. The rope passes through a belay device that is often attached to the harness of another person, the “belayer”. The belayer operates the belay device and typically remains at a stable point while the climber ascends. When the climber is “lead” climbing, the climber drags the rope up the rock as he ascends. At various points during the ascent, the climber clips the rope into metal loops (carabiners) that, in turn, are attached to the surface of the rock. When the climber is “top-rope” climbing, the rope extends down toward the climber from above. In the case of lead climbing, the belayer feeds out rope as the climber ascends. In the case of top-rope climbing, the belayer takes in rope as the climber ascends. In either case, if the climber falls, the belayer must grasp the rope securely by means of the belay device. The fall is therefore stopped by means of the belay device and the climber comes to rest suspended from above by the rope. Thereafter, the belayer may gently lower the climber to the ground by operating the belay device so as to gradually release tension on the rope. Anyone experienced in rock climbing is familiar with this practice and with the various forms of belay devices.
Over the years many devices have been developed to grip a rope and to control the rate of movement of rope, and many of these devices have been used for the purpose of belaying or for the very similar purpose of descending. Much of the patented prior art deals with descenders, many of which can also be used as belay devices. A descender is designed to lower a person or object in a controlled fashion.
The devices of the prior art can be broadly categorized into two classes:
The first class, manual belay devices, consists of relatively simple devices that contain no moving parts. These devices, many of which are very effective, rely entirely upon frictional forces developed within a torturous path through which the rope runs. A positive attribute of this class is that these devices are inexpensive since they are based on simple designs and contain no moving parts. On the negative side, these devices require action on the part of the belayer in order to stop a fall. If the belayer is inattentive or looses his grip, the result can be disastrous. Also on the negative side, it is difficult to feed rope quickly through these devices due to the torturous path of the rope. Examples include U.S. Pat. No. D413,786 to Graham, U.S. Pat. No. 5,217,092 to Potter, and U.S. Pat. No. 5,671,822 to Phillips.
The second class, auto-locking belay devices, generally consist of relatively more complicated designs, often with moving parts, that have the benefit of requiring no action on the part of a belayer in order to stop a fall. Often, such devices consist of one or more cams over which the rope runs. The cams either have an off-center axis of rotation or a variable radius that increases as the cam rotates. At least one such cam in each such device is usually designed such that, under normal climbing conditions, the rope slips over the surface of the cam and the cam remains stationary but, in the event the climber falls, the friction developed by the rapid passage of the rope along the cam surface causes the cam to rotate. Due to the shape of the cam, rotation thereof causes the rope to be pinched and stops the rope. These rotating cams are often spring loaded so as to resist rotation until a certain threshold frictional force has been achieved. A positive attribute of this class is that these devices require little or no action on the part of the belayer in order to stop a fall. On the negative side, these devices are relatively more expensive since they are more complicated designs and often have multiple moving parts. The presence of a moving part usually implies the requirement for manual labor in the assembly of that part which, in turn, implies relatively higher manufacturing cost. Examples of these auto-locking devices include U.S. Pat. No. 4,531,610 to Fertier et. al., U.S. Pat. No. 5,360,083 to Hede, U.S. Pat. No. 5,577,576 to Petzl et al., and U.S. Pat. No. 5,597,052 to Rogleja.
At least one device has been developed which achieves the enhanced functionality of the auto-locking class of belay devices, while maintaining the relative simplicity of design found in the manual class of belay devices. The device presented in US Patent Application Publication No. US 2003/0034203 A1 by Hewlett et al. is such a device. Hewlett's device is auto-locking yet has no moving parts.
All of the auto-locking belay devices contain two braking surfaces which, in one configuration are sufficiently separated so as to allow a rope to easily pass between them, and in another configuration are sufficiently close so as to pinch a rope that is positioned between them. The forces on the rope from the fall of a climber cause the device to shift from the former configuration to the latter configuration, the pinch on the rope by the braking surfaces thus stopping the rope and arresting the fall of a climber. Since the two braking surfaces must move relative to each other in order to pinch the rope, it would seem unlikely that an auto-locking belay device could be made which has no moving parts. Hewlett's device overcomes this apparent restriction by relying on the attachment carabiner to provide one of the braking surfaces. Therefore, although Hewlett's device itself has no moving parts, the device moves with respect to its attachment carbiner in the event of a fall by a climber, thus causing two braking surfaces to move with respect to each other, one braking surface being on the carabiner and the other being within Hewlett's device.
In order for an auto-locking belay device to work well, there are a great many design characteristics that must be optimized and that often appear to be in conflict with each other. Some ideal characteristics of a belay device are:
It should be simple to operate. A device that is simple to operate allows the belayer to pay more attention to the climber and less to the operation of the device.
It should be strong, yet lightweight and small. Since climbers often have to carry a substantial amount of equipment, weight and size are important factors.
It should grip the rope very tightly when the climber falls. Sometimes climbers fall from heights significantly above their last rope attachment point. The device must be able to stop a heavy climber who has been in a free fall.
It should allow easy passage of the rope as the climber is climbing.
It should render the climber in a safe position should the belayer accidentally loose his grip either on the device itself or on the rope.
It should allow for the belayer to easily lower the climber in a controlled fashion.
Its manufacturing costs should be such that it is affordable.
It should not cause undue wear on the rope.
These desired attributes can lead to design features that are in conflict with each other. For example:                a very strong device might be too large or too heavy;        a device that grips the rope very tightly might not allow the belayer to easily lower the climber;        a device that grips the rope very tightly might cause excessive wear on the rope;        a device that allows easy passage of the rope might not grip the rope sufficiently tightly when a climber falls;        a device which renders the climber in a safe position even if the belayer looses his grip, might have excessive manufacturing costs due to greater complexity.        
Although Hewlett's device offers an innovative approach to a simple auto-locking belay device, it poses design restrictions that limit the ability to optimize a device for all of the desired characteristics. An important feature of Hewlett's device is an elongated opening through which the carabiner is clipped. When the carabiner is positioned in one portion of this opening, a rope is able to pass freely. When the carabiner is positioned in another portion of this opening, the rope is pinched and prevented from moving. The rope forces resulting from the fall of a climber cause the carabiner to move from the first position within the opening to the second position within the opening. Hewlett's device thus stops the rope by causing the rope to be pinched by the tubing of the carabiner, the carabiner tubing lying across the rope and pinching the rope against a surface of Hewlett's device.
One negative aspect of Hewlett's device is that the size of the carabiner braking surface is relatively small. Since the carabiner tubing which forms the braking surface passes across the rope and is directly perpendicular to the path of the rope, the size of that braking surface is limited based on the tubing radius of a standard locking carabiner. It is possible that a significant force, transmitted to such a small braking surface, can cause damage to the rope.
Another negative aspect of Hewlett's device is that it greatly limits design flexibility with respect to the physical concept of mechanical advantage. In the locked configuration, the carabiner lies directly above, and in contact with, the rope. Also, the centerline of the carabiner tubing that passes through the opening serves as the axis of rotation around which Hewlett's device can rotate with respect to the carbiner. This means that the distance between the axis of rotation and the rope pinch point is equal to the radius of the carabiner tubing. As will be explained in the description of the subject invention, the aforementioned distance is a critical variable in determining the mechanical advantage between the force on the rope from a fallen climber and the pinch force exerted on the rope by the belay device.
The devices described in the above mentioned patents, do not disclose, teach or illustrate the unique structure, function and advantage of the subject belay device.